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* [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
@ 2021-01-26 17:33 o.mandel at menlosystems dot com
2021-01-26 17:33 ` [Bug c++/98841] " o.mandel at menlosystems dot com
` (10 more replies)
0 siblings, 11 replies; 12+ messages in thread
From: o.mandel at menlosystems dot com @ 2021-01-26 17:33 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
Bug ID: 98841
Summary: wrong ‘operator=’ should return a reference to ‘*this’
[-Weffc++]
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: o.mandel at menlosystems dot com
Target Milestone: ---
Created attachment 50059
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50059&action=edit
Console output of version 8.3.0
I get unexpected warnings about "'operator=' should return a reference to
'*this' [-Weffc++]".
This happens for at least versions 8.3.0 and 10.2.0 of g++. The output of the
following command is attached for both versions:
g++ -v -save-temps -Weffc++ -c t.cpp
In the minimal demo used here this only happens for a template member function,
but in larger code it can also be observed for a plain member function: see
e.g. https://github.com/jbeder/yaml-cpp/issues/970
This might be the same issue as mentioned in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84364#c9 (why the comment asked
for that ticket to be reopened)?
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
@ 2021-01-26 17:33 ` o.mandel at menlosystems dot com
2021-01-26 17:34 ` o.mandel at menlosystems dot com
` (9 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: o.mandel at menlosystems dot com @ 2021-01-26 17:33 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
--- Comment #1 from Olaf Mandel <o.mandel at menlosystems dot com> ---
Created attachment 50060
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50060&action=edit
Preprocessed source file of version 8.3.0
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
2021-01-26 17:33 ` [Bug c++/98841] " o.mandel at menlosystems dot com
@ 2021-01-26 17:34 ` o.mandel at menlosystems dot com
2021-01-26 17:35 ` o.mandel at menlosystems dot com
` (8 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: o.mandel at menlosystems dot com @ 2021-01-26 17:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
--- Comment #2 from Olaf Mandel <o.mandel at menlosystems dot com> ---
Created attachment 50061
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50061&action=edit
Console output of version 10.2.0
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
2021-01-26 17:33 ` [Bug c++/98841] " o.mandel at menlosystems dot com
2021-01-26 17:34 ` o.mandel at menlosystems dot com
@ 2021-01-26 17:35 ` o.mandel at menlosystems dot com
2021-01-26 17:47 ` redi at gcc dot gnu.org
` (7 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: o.mandel at menlosystems dot com @ 2021-01-26 17:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
--- Comment #3 from Olaf Mandel <o.mandel at menlosystems dot com> ---
Created attachment 50062
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50062&action=edit
Preprocessed source file of version 10.2.0
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
` (2 preceding siblings ...)
2021-01-26 17:35 ` o.mandel at menlosystems dot com
@ 2021-01-26 17:47 ` redi at gcc dot gnu.org
2021-01-26 19:04 ` pinskia at gcc dot gnu.org
` (6 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: redi at gcc dot gnu.org @ 2021-01-26 17:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2021-01-26
Keywords| |diagnostic
Ever confirmed|0 |1
Blocks| |81930
Status|UNCONFIRMED |NEW
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81930
[Bug 81930] [meta-bug] Issues with -Weffc++
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
` (3 preceding siblings ...)
2021-01-26 17:47 ` redi at gcc dot gnu.org
@ 2021-01-26 19:04 ` pinskia at gcc dot gnu.org
2021-01-26 19:25 ` jakub at gcc dot gnu.org
` (5 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-01-26 19:04 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
-Weffc++ is really a bad option in general ....
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
` (4 preceding siblings ...)
2021-01-26 19:04 ` pinskia at gcc dot gnu.org
@ 2021-01-26 19:25 ` jakub at gcc dot gnu.org
2021-01-27 10:42 ` jakub at gcc dot gnu.org
` (4 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: jakub at gcc dot gnu.org @ 2021-01-26 19:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
/* Returning '*this' is obviously OK. */
if (retval == current_class_ref)
warn = false;
assumes that retval and current_class_ref must be equal, but that isn't clearly
the case, they can be different pointers.
The retval is created in templates here in:
#6 0x0000000000e0a273 in build_min (code=INDIRECT_REF, tt=<record_type
0x7fffea1b4000 Foo>) at ../../gcc/cp/tree.c:3455
#7 0x0000000000e3548c in build_x_indirect_ref (loc=251460, expr=<nop_expr
0x7fffea19ea00>, errorstring=RO_UNARY_STAR, complain=3) at
../../gcc/cp/typeck.c:3329
So, I wonder if we shouldn't do:
if (retval == current_class_ref
|| operand_equal_p (retval, current_class_ref, 0))
warn = false;
instead.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
` (5 preceding siblings ...)
2021-01-26 19:25 ` jakub at gcc dot gnu.org
@ 2021-01-27 10:42 ` jakub at gcc dot gnu.org
2021-01-27 17:46 ` o.mandel at menlosystems dot com
` (3 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: jakub at gcc dot gnu.org @ 2021-01-27 10:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 50067
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50067&action=edit
gcc11-pr98841.patch
Untested fix.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
` (6 preceding siblings ...)
2021-01-27 10:42 ` jakub at gcc dot gnu.org
@ 2021-01-27 17:46 ` o.mandel at menlosystems dot com
2021-01-28 23:40 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: o.mandel at menlosystems dot com @ 2021-01-27 17:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
--- Comment #7 from Olaf Mandel <o.mandel at menlosystems dot com> ---
(In reply to Olaf Mandel from comment #0)
> In the minimal demo used here this only happens for a template member
> function, but in larger code it can also be observed for a plain member
> function: see e.g. https://github.com/jbeder/yaml-cpp/issues/970
>
I have to retract that statement: I cannot reproduce this and the two line
numbers in the larger code in question are very similar: 212 and 221. Maybe I
just confused them?
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
` (7 preceding siblings ...)
2021-01-27 17:46 ` o.mandel at menlosystems dot com
@ 2021-01-28 23:40 ` cvs-commit at gcc dot gnu.org
2021-01-28 23:41 ` jakub at gcc dot gnu.org
2021-01-29 9:15 ` o.mandel at menlosystems dot com
10 siblings, 0 replies; 12+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-01-28 23:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:
https://gcc.gnu.org/g:850a8ec54c4310d779004299bf9a0dec52324e9e
commit r11-6964-g850a8ec54c4310d779004299bf9a0dec52324e9e
Author: Jakub Jelinek <jakub@redhat.com>
Date: Fri Jan 29 00:39:00 2021 +0100
c++: Fix -Weffc++ in templates [PR98841]
We emit a bogus warning on the following testcase, suggesting that the
operator should return *this even when it does that already.
The problem is that normally cp_build_indirect_ref_1 ensures that *this
is folded as current_class_ref, but in templates (if return type is
non-dependent, otherwise check_return_expr doesn't check it) it didn't
go through cp_build_indirect_ref_1, but just built another INDIRECT_REF.
Which means it then doesn't compare pointer-equal to current_class_ref.
The following patch fixes it by doing in build_x_indirect_ref for
*this what cp_build_indirect_ref_1 would do.
2021-01-28 Jakub Jelinek <jakub@redhat.com>
PR c++/98841
* typeck.c (build_x_indirect_ref): For *this, return
current_class_ref.
* g++.dg/warn/effc5.C: New test.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
` (8 preceding siblings ...)
2021-01-28 23:40 ` cvs-commit at gcc dot gnu.org
@ 2021-01-28 23:41 ` jakub at gcc dot gnu.org
2021-01-29 9:15 ` o.mandel at menlosystems dot com
10 siblings, 0 replies; 12+ messages in thread
From: jakub at gcc dot gnu.org @ 2021-01-28 23:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for GCC 11.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c++/98841] wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++]
2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
` (9 preceding siblings ...)
2021-01-28 23:41 ` jakub at gcc dot gnu.org
@ 2021-01-29 9:15 ` o.mandel at menlosystems dot com
10 siblings, 0 replies; 12+ messages in thread
From: o.mandel at menlosystems dot com @ 2021-01-29 9:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98841
--- Comment #10 from Olaf Mandel <o.mandel at menlosystems dot com> ---
Thank you, that was quick!
Though, didn't this miss the [end of stage 3 development][1] by 11 days?
[1]: <https://gcc.gnu.org/develop.html#timeline>
^ permalink raw reply [flat|nested] 12+ messages in thread
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2021-01-26 17:33 [Bug c++/98841] New: wrong ‘operator=’ should return a reference to ‘*this’ [-Weffc++] o.mandel at menlosystems dot com
2021-01-26 17:33 ` [Bug c++/98841] " o.mandel at menlosystems dot com
2021-01-26 17:34 ` o.mandel at menlosystems dot com
2021-01-26 17:35 ` o.mandel at menlosystems dot com
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